An experimental investigation into solids conveying
AN EXPERIMENTAL INVESTIGATION INTO SOLIDS FEEDINGCHARACTERISTICS OF A SINGLE PIECE BARREL WITH INTEGRAL FEEDPORT DESIGN VS A STANDARD TWO PIECE WATER COOLED FEEDBLOCK AND BARREL CONFIGURATION. Walter S. Smith Robert A. Sickles Luke A. Miller Timothy W. Womer Xaloy Corporation, New Castle, PA Abstract L/D along its axial length. Figure 3 shows the integral feed block configuration.Differences in solids conveying, screw pressure profilegeneration, output and melt temperature varies between Figure 4 shows the 711mm (28”) Flex-lip Sheet die and thesingle piece barrel with integral feedport design and two Slide plate screen changer. The die was set to 1.4 mmpiece water cooled feedblock and barrel designs. Two (.055”). The Screen Changer was loaded with a breakerdifferent resins will be studied using the same screw plate and a 20/40/60/20 screen pack. A immersion meltdesign for each barrel configuration. probe was inserted in the melt stream between the screen changer and die. Introduction A low shear barrier screw with mixer was used for all testing. This screw was specifically designed forExtruders can be designed with either a standard two- polypropylene extrusion with a longer feed section.piece water-cooled feedblock- barrel configuration, orwith an integral feed port - thru barrel configuration. This A Fluke Data Acquisition System was used to acquire allpaper will explore the processing differences between data from the process. It will be referred to as NetDAQ.these two different barrel configurations under the samecontrolled processing conditions and equipment. Resins Equipment Two resins were used for this study. • 100 % HDPE Regrind (540 kg/m3 bulk density)The extruder used for this study was a 90mm (3.5”) x 0.3 MI24:1 NRM Extruder with five-barrel water-cooled • 100 % PP Regrind (384 kg/m3 bulk density) 2.0temperature zones. It is equipped with a 112 kW (150 MIHp) DC motor. Max screw speed is 129 rpm. Figure 1shows the extruder with (11) melt pressure transducerslocated every 2 L/D down the axial length of the barrel. Experimental ProcedureThe standard two-piece configuration consisted of a Each of the two resins was extruded using the integral feedseparate water-cooled feedblock with a flanged extrusion port, with water cooled feed block; and the standard two-barrel bolted on the downstream end of the feed block. piece ductile iron water-cooled feed block for a total of fourThis barrel also has (11) melt transducers to record the twenty-seven minute runs.internal pressures at every (2) L/D along the axial lengthof the barrel. Figure 2 shows the barrel feedblock For each test, the barrel and screw were completely cleaned.configuration. The die was pre-heated two hours prior to each twenty- seven minute test, and the barrel was pre-heated toThe integral configuration consisted of an extrusion barrel processing temperature for one hour before the testingthat fits through a water-cooled feed block with a feed started. Steady thermal conditions were then assumed toport machine directly into the cylinder. This barrel also prevail throughout each of the four twenty-seven minutehas (11) melt pressure transducers located at every (2) tests.
amp draw at all (5) screw speeds for both barrelThe two resins were run on the standard two-piece configurations running HDPE. Again, the increase in motorfeedblock and barrel configuration. The feedblock was load is directly attributed to the increase in throughput rate.water-cooled. Once these trials were completed the barreland feedblock were changed to the single piece barrel The barrel pressure profiles for both screws running HDPEwith integral feedport. The same “hump” barrel at 125 screw rpm on both barrel configurations are shown intemperature profiles were used for same barrel type and Figure 12.resin tested along with the same feed throat watertemperature. See Chart 1 for barrel temperature profiles. The integral feed port configuration produced both higher rates and melt temperatures for running HDPE. See FigureEach test included screw speeds of 25, 50, 75, 100, and 13 for an output/melt temperature comparison. The125 rpm. Melt temperature was checked at each screw temperature of the integral barrel, in the area under the feedrpm using a hand held IR gun, melt probe, and immersion zone was also measured and recorded at all (5) screwprobe. Three one-minute sheet samples were taken at each speeds. See figure 14 for a screw rpm vs. feed zoneset rpm to calculate screw output rate. The barrel temperature graph.pressure, immersion probe, screw speed and motor ampswere all monitored and recorded at one-second intervals Discussion of Data and Resultson the NetDAQ.The data were then extracted from the NetDAQ and The major difference between the (2) machinecompiled with a spreadsheet program. configurations is the thermal isolation of the feed port in the standard (2) piece configuration. Heat from the barrel does Presentation of Data and Results not travel as easily back to the first (2) turns of the feed port area in the standard two-piece configuration. Both barrel Regarding the PP trials: The integral feed throat pressure profiles, for HDPE and PP; confirm that the screwconfiguration produced more output at every screw speed, builds higher pressure much earlier in the feed section of thethan the standard two piece barrel and feed block screw. This higher-pressure buildup can be attributed toconfiguration. The output increased across all screw more resin melting and a higher coefficient of frictionspeeds for the integral configuration. See Figure 5 for between the pellet and the barrel is causing the resin to stickoutput rates for the (5) screw speeds comparing the (2) to the barrel sooner and improve solids conveying. Thisbarrel configurations. As suspected, the amp draw was up extra heat in the feed port area migrating back from the firstat all (5) screw speeds on the integral configuration barrel zone; increases the coefficient of friction between thecompared to the standard (2) piece configuration, because resins an internal diameter of the barrel, thus enhancing theof the increase in output. See Figure 6 for the motor amp solids conveying capacity of the screw. This is the maindraw at the all (5) screw speeds for both barrel reason for the increase in output of both of the screws andconfigurations for running PP. both of the resins in the integral feed throat machine configuration versus the standard configuration.The barrel pressure profiles for PP at 125 Screw rpm onboth configurations are shown in Figure 7. The temperature range of the feed port area in the integral PP trials was 69 C thru 62.5 C, versus a constant 22 C for The integral feed port configurations produced both the standard (2) piece machine configuration. This recordedhigher rates and higher melt temperatures for running PP. temperature range depended on the screw speed. The fasterSee Figure 8 for an output vs. melt temperature the screw rotated, the lower the recorded temperature in thecomparison. The temperature of the integral barrel, in the feed port area fell. The recorded temperature range of thearea under the feed zone was also measured and recorded feed port area in the integral HDPE trials was 71 C thru 59at all (5) screw speeds. See Figure 9 for a screw rpm vs. C, versus a constant 22 C for the standard (2) piecefeed zone temperature graph. configuration. This recorded temperature range also depended on the screw speed. The faster the screw speed,Regarding the HDPE trials: The integral feed throat the lower the recorded temperature of the feed port area fell.configuration produced more output rate at every screw It can be assumed at greater screw speeds, more roomspeed, than the standard two piece barrel and feed block temperature resin goes thru this area, pulling more excessconfiguration. The output increased across all the screw heat out, and thus reducing the barrel temperature in thisspeeds for the integral configuration. See Figure 10 for critical processing area.output rates for the (5) screw speeds comparing the (2)barrel configurations. The amp draw was also up at all (5) The effect of the higher temperatures feed port area, in thescrew speeds for the integral configuration compared to integral machine configuration; had a much greaterthe standard configuration. See Figure 11 for the motor influence on the output of each screw, especially when
running the PP. There was a 19.47% - 6.91% increase in Z1 Z2 Z3 Z4 Z5 S/C AD D1 D2 D3output in the PP trials, depending on screw speed; as HDPE 380 450 440 420 400 400 430 430 430 430compared to a 7.63% - 3.72% increase in output in the PP 400 470 450 430 410 410 430 430 430 430HDPE trials. Chart 1-Processing Temperatures Conclusions 1. Heat migration using an integral barrel-feed port barrel configuration will aid in solids conveying and increased output in the extrusion process, because of the increase in coefficient of friction between the pellet and the barrel wall in the feed section of the screw. 2. The increase in output in this study, attributed to the integral barrel configuration; is more pronounced when running PP and opposed to HDPE. 3. Care must be taken when designing for an integral barrel configuration, because of the excess power required from the motor resulting from the increase in solids conveying and screw output. Figure 1-90mm x 24:1 NRM Extruder 4. Although the higher temperatures in the integral barrel configuration aid in solids conveying; temperatures over 90 C should be avoided to prevent resin from melting in the hopper producing a melt block or bridging situation. 5. Modified barrel temperature profiles may be needed to improve the overall melt temperature of the process, which was not evaluated in this Figure 2-90mm Barrel Feedblock Configuration study. 6. Integral feed throats improve alignment between the barrel and gearbox, because one connection point has been eliminated. 7. Venting of integral feedthroat barrels is more difficult due to the improved solids conveying that occurs. Additional testing will be done on this subject and reported at a later date. Figure 3-90mm Integral Feedblock ConfigurationReferences 1. C. Rauwendaal, Polymer Extrusion, Hanser Publishers, NY, 1986 2. E. Steward; W. A. Kramer, Air vs. Water Cooled Single Screw Extruders, ANTEC 2003 3. J. Wortberg; T. Schroer, Novel Barrel Heating with Natural Gas, ANTEC 2003
Integral Feedblock Compared to The Standard Feedblock on PP+EVOH Screen Changer 16000 14000 12000 10000 Pressure (KPa) 8000 6000 4000 Integral Standard 2000 Die 0 0 57 71 92 108 128 144 164 181 199 221 240 Pressure Transducer Location from Face of Drive Shaft (cm) Figure 7-Barrel Pressure of PP at 125RPM Figure 4-Die, Screen Changer Effect of Rate on Melt Temperature on PP Output (Kg/Hr) of PP 200 255 200.00 25% Integral Rate Standard Rate Integral Melt Temp Standard Melt Temp Integral Rate Standard Rate Rate 180 250 180.00 160 245 160.00 20% 19.47% 140 140.00 240 K g/H R (B ar G rap h) °C (Line G raph ) Rate Difference 14.98% 120 120.00 15% 235Kg/Hr 100 100.00 230 80.00 10% 80 225 60.00 7.16% 6.91% 60 5.25% 220 40.00 5% 40 20.00 20 215 0.00 0% 0 210 25 50 75 100 125 25 50 75 100 125 RPM RPM Figure 5-Output of PP Figure 8-Effect of Rate on Melt Temperature on PP Effect of Rate on Amps Using PP Temperature of Feed Zone on the Integral Barrel PP 200 100 Integral Rate Standard Rate Integral Amps Standard Amps 180 90 69 68 160 80 67 140 70 A m p s (L in e G rap h)K g/H r (B ar G rap h) 66 120 60 65 100 50 °C 64 80 40 63 60 30 62 40 20 61 20 10 60 0 0 25 50 75 100 125 59 RPM 25 50 75 100 125 RPM Figure 6-Effect of Rate on Amps-PP Figure 9-Temperature of Feed on Integral Barrel-PP
Output (Kg/Hr) of HDPE Effect of Rate on Melt Temperature on HDPE 240 250 250.00 9% Integral Rate Standard Rate Integral Melt Temp Standard Melt Temp Integral Rate Standard Rate Rate 220 245 8% 200 7.63% 240 200.00 180 7% 235 160 Kg/HR (Bar Graph) 6% °C (Line Graph) 5.53% R ate Difference 230 140 150.00 5% K g/H r 3.93% 120 225 4.33% 3.72% 4% 100 220 100.00 80 3% 215 60 2% 210 50.00 40 1% 205 20 0 200 0.00 0% 25 50 75 100 125 25 50 75 100 125 RPM RPM Figure 13-Effect of Rate on Melt Figure 10-Output of HDPE Temperature on HDPE Effect of Rate on Amps Using HDPE Temperature of Feed Zone on the Integral Barrel -HDPE 250 140 Integral Rate Standard Rate Integral Amps Standard Amps 72 120 70 200 100 68 Am ps (Line G raph) K g/Hr (Bar Graph) 66 150 80 64 60 °C 100 62 60 40 50 58 20 56 0 0 54 25 50 75 100 125 RPM 52 25 50 75 100 125 Figure 11-Effect of Rate on Amps-HDPE RPM Figure 14-Temperature of Feed on Integral Integral Feedblock Compared to The Standard Feedblock on HDPE at 125 RPM Barrel-HDPE 20000 18000 16000 14000Pressure (KPa) 12000 10000 8000 6000 Integral 4000 Standard 2000 0 0 57 71 92 108 128 144 164 181 199 221 240 Pressure Transducer Location from Face of Drive Shaft (cm) Figure 12-Barrel Pressure of HDPE at 125RPM